1. Field of the Invention
This invention relates to an edge polisher for mirror-polishing chamfered edge portions of a work, for example, chamfered marginal edge portions of semiconductor wafers, glass sheets, quartz sheets, ceramic substrates and the like.
2. Description of the Prior Art
For instance, semiconductor wafers such as silicon wafers normally have their marginal edges chamfered for the purpose of preventing edge chipping and precluding crowning in epitaxial growth.
However, subsequent to the chamfering which employs diamond abrasive grains for the grinding operation, a machining distortion layer tends to remain on the work, giving rise to various problems as follows. Namely, such a machining distortion layer which remains after a grinding operation is likely to invite the so-called crystal sliding phenomenon in a device process due to the thermal stress resulting from repeated heat treatments, or fracturing of edge portions by the impacts imposed by a quartz board on which the work is transferred between various processes, producing refuse of fractured fragments which would lead to a drop in yield, defoliation of oxidation film, degradation in washability, deterioration of resist flows at edge portions and so forth.
Therefore, it has been the usual practice to remove such machining distortion layers by etching. However, etched surfaces contain wavy or scale-like irregularities which are susceptible to fouling. Especially, even a slight degree of fouling which remains in a chamfered portion might diffuse to the entire wafer in a device process to deteriorate the wafer characteristics.
Under these circumstances, the present inventors succeeded in solving these problems by developing an apparatus for mirror-polishing chamfered edge portions of wafers, as proposed in Japanese Laid-Open Patent Application 64-71656.
The polishing apparatus of the above-mentioned application, which is arranged to polish wafers one by one, has an advantage that it can be applied in a compact form for small-scale wafer treatments, but in terms of efficiency it is unsuitable for wafer treatments on a large scale. Therefore, there have been demands for a polisher which is capable of concurrently treating a plural number of wafers.